(1) Field of the Invention
The present invention relates to a method and the device for implementing the pasteurization or sterilization of products, in particular under flexible or rigid closed packaging.
The purpose of the sterilization and pasteurization are to increase the preservation of food. These operations require a rise in temperature, which is generally followed by a phase of cooling of the product.
During these operations, the rise in temperature creates an increase in pressure inside the packaging. It is then necessary to compensate for this internal pressure by a pressure applied to the outside of the packaging.
(2) Description of the Prior Art
The existing methods and devices thus require a chamber maintained under pressure when sterilization, pasteurization and cooling operations are carried out. An existing device is a chamber in which the products are placed through inlet and/or outlet means. Said chamber is then pressurized, the increase in pressure being carried out as the rise in temperature inside the closed chamber progresses. The temperature and the pressure are then decreased and the products leave the chamber through the inlet and/or outlet means. Such devices are known from the state of the art, such as the autoclaves.
The drawback of these devices is the discontinuous aspect of the method. In order to cope with this discontinuity, a hydrostatic installation was designed to provide the possibility of sterilizing or pasteurizing the products continuously.
The hydrostatic principle consists in causing the products to be sterilized or pasteurized to pass from the top to the bottom of a column of hydrostatic heating fluid, the surface of the fluid column being open to the atmosphere, and therefore subjected to the atmospheric pressure. As the product flows downwards in the column, it is subjected to an increasing pressure applied by the fluid, compensating for the internal increase in pressure due to the rise in temperature. A maximum pressure can be applied in the lower portion of the column and can vary proportionally to the height of liquid in the column. The product must flow upwards under decreasing pressure while being cooled.
A solution for the implementation of this principle consists in placing a median wall in order to separate the column of heating fluid into two, like a siphon, thus forming a circuit within the column. The products are then conveyed from an inlet located at the top of the column, on one side of the wall, to the bottom, being submitted to an increasing pressure, then from the bottom towards an outlet located at the top of the column, on other side of the wall, being submitted to a decreasing pressure.
In order to obtain a sufficient pressure with respect to the sterilization or pasteurization temperature, the height of the installations would be of about ten meters and hence difficult to be installed. Moreover, the temperature of the liquid of a heating column can difficultly vary from the top to the bottom of the column and the products require a phase of cooling under pressure.
In order to cope with these drawbacks, there has been devised an installation in the form of a chamber comprising a hydrostatic heating compartment separated from a hydrostatic cooling compartment by an intermediate pressurizing compartment, this separation being necessary to avoid the thermal exchange and dissipations between the heating and cooling compartments.
The heating and cooling compartments are each comprised of at least one hydrostatic fluid column as described above. In the case of a compartment including several consecutive columns, the pressure corresponding to the height of liquid of a first column is passed on the following column, and so on, from the outside of the chamber under atmospheric pressure to the intermediate compartment.
The intermediate pressurizing compartment serves as a heat insulator between the two other hydrostatic compartments and includes pressurizing means for the intermediate compartment.
Without application of pressure, the levels are balanced on both sides of the median wall of each column. The increase in pressure inside the intermediate compartment applies a pressure on the surfaces of liquid of the columns adjacent to that the compartment. When the pressure applied is sufficient, the level of the column lowers at the side of the partition where the pressure is applied and rises at the other side.
The rising of the level of liquid in the columns creates a pressure on an air column separating two consecutive water columns. This pressure, when it is sufficiently high, causes the level of liquid of the following column to lower and the level located at the other side of the median wall of this column to rise. And so on for any adjacent column.
The pressure applied in the intermediate compartment thus passes on each following column. The pressure in each column depends on the height of liquid to be moved in said column. The pressure applied to each column of liquid decreases from one column to the next one in the direction from the center to the inlet and outlet ends of the chamber, this reduction resulting from the total volume of liquid to be moved being increasingly less as the number of columns diminishes from the intermediate compartment to the inlet or the outlet of the chamber, under atmospheric pressure.
The pressure provided by the intermediate compartment can be increased or decreased according to the needs, according to the type of the products and of their sterilization or pasteurization temperature. However, if this pressure exceeds a maximum value, the level of liquid of the columns will overflow. The maximum pressure applicable within the device is thus increased by the height and the number of columns during manufacture.
The known devices for continuous sterilization or pasteurization thus have the drawback of having a maximum pressure fixed during manufacture and, hence, a maximum pasteurization or sterilization temperature. Under these circumstances, it can happen that for the sterilization or the pasteurization of a line of goods, a large majority of them require an installation the heating compartment of which would include a limited number of hydrostatic columns, while, to cover a minority of products, the counter-pressure to be applied would be such that it would be necessary to substantially increase the number of these columns, which would result into a substantial increase in the cost of the installation.
In U.S. Pat. No. 3,340,791 is disclosed a device for the sterilization of products, in particular glass containers, which is nevertheless without part of these drawbacks. To this end, it comprises a chamber under pressure in which circulates an endless conveyor conveying of products to be sterilized from a chamber under high air pressure to a hydrostatic heating chamber, then through a sterilization chamber, also pressurized, and to a hydrostatic cooling chamber, to finally return into said pressurized chamber. In this connection, said chamber comprises means for loading and unloading said conveyor, which are in the form of a rotary valve under pressure at the inlet and the outlet of the chamber. The hydrostatic chambers are in the form of a compartment, filled with hydrostatic liquid, arranged vertically and a portion of which is lengthened horizontally in order to heat or cool the products under constant pressure. In this connection, it should be noted that these hydrostatic chambers are heated so that at their upper ends, emerging into the sterilization chamber, the liquid is hot, while at their lower end, emerging into the chamber under high air pressure, the liquid is colder. In this way, the products are gradually heated during their passing into the hydrostatic heating chamber and slowly cooled during their being conveyed through the cooling chamber.
Even though it allows to vary the pressure within the chamber by increasing or decreasing the pressure of the highly pressurized chamber, accessible through valves, at the same time as the pressure of the sterilization chamber, this device is aimed at sterilizing solid packaging, such as a glass bottle and is not suitable for flexible or partly flexible packaging. Hence, it has the drawback of applying too high a pressure on the products, the highest in the whole chamber, right from their entering into the pressure chamber, so that flexible packaging can be damaged.
Moreover, the devices of the state of the art generally have the drawback that once the process has been launched, there is little possibility of modifying the parameters, such as the pressure and the temperatures the products are submitted to, but more particularly the sterilization, heating and/or cooling time.